1. Technical Field
The present invention relates to inside printing of flexible packages constructed from either a vertical or horizontal form and fill packaging machine, and the method for making same, that provides for a graphics presentation inside the package for promotional or other purposes. The invention allows for use of existing film converter and packaging technology to produce a package that meets present required packaging guidelines with minimal increased costs.
2. Description of Related Art
Vertical form, fill, and seal packaging machines are commonly used in the snack food industry for forming, filling, and sealing bags of chips and other like products. Such packaging machines take a packaging film from a sheet roll and forms the film into a vertical tube around a product delivery cylinder. The vertical tube is vertically sealed along its length to form a back seal. The machine applies a pair of heat-sealing jaws or facings against the tube to form a transverse seal. This transverse seal acts as the top seal on the bag below and the bottom seal on the package being filled and formed above. The product to be packaged, such as potato chips, is dropped through the product delivery cylinder and formed tube and is held within the tube above the bottom transverse seal. After the package has been filled, the film tube is pushed downward to draw out another package length. A transverse seal is formed above the product, thus sealing it within the film tube and forming a package of product. The package below said transverse seal is separated from the rest of the film tube by cutting across the sealed area.
The packaging film used in such process is typically a composite polymer material produced by a film converter. For example, one prior art composite film used for packaging potato chips and like products is illustrated in FIG. 1a, which is a schematic of a cross-section of the film illustrating each individual substantive layer. FIG. 1a shows an inside, or product side, layer 16 which typically comprises metalized oriented polypropylene (“OPP”) or metalized polyethylene terephthalate (“PET”). This is followed by a laminate layer 14, typically a polyethylene extrusion, and an ink or graphics layer 12. The ink layer 12 is typically used for the presentation of graphics that can be viewed through a transparent outside layer 10, which layer 10 is typically OPP or PET.
Subsequent to being produced by the converter, the composite polymer film is sent to a slitter where it is cut into three strips. Each strip can then be wound into a sheet roll prior to being sent to a vertical form and fill machine, or bagmaker.
The prior art film composition shown in FIG. 1a is ideally suited for use on vertical form and fill machines for the packaging of food products. The metalized inside layer 16, which is usually metalized with a thin layer of aluminum, provides excellent barrier properties. The use of OPP or PET for the outside layer 10 and the inside layer 16 further makes it possible to heat seal any surface of the film to any other surface in forming either the transverse seals or back seal of a package.
Typical back seals formed using the film composition shown in FIG. 1a are illustrated in FIGS. 2a and 2b. FIG. 2a is a schematic of a “lap seal” embodiment of a back seal being formed on a tube of film. FIG. 2b illustrates a “fin seal” embodiment of a back seal being formed on a tube of film.
With reference to FIG. 2a, a portion of the inside metalized layer 26 is mated with a portion of the outside layer 20 in the area indicated by the arrows to form a lap seal. The seal in this area is accomplished by applying heat and pressure to the film in such area. In the embodiment shown in FIG. 2b, the inside layer 36 is folded over and then sealed on itself in the area indicated by the arrows. Again, this seal is accomplished by the application of heat and pressure to the film in the area illustrated.
As noted, a benefit of both the prior art fin seal and lap seal design is the containment of the product in the package by a barrier layer (the metalized inside layer) and an effective seal that keeps out light, oxygen, and moisture. It may be desirable to provide a graphics capability inside a sealed package. This would allow for promotional information or coupons to be maintained inside the package and only accessible after the consumer has opened the package. For example, a promotional prize campaign could be offered with the prize announcements being maintained inside the package. Likewise, coupons offering product rebate rewards, promotional prize points, or discounts on products could be maintained within the sealed package. Food grade inks, however, do not adhere well to the barrier layer.
One prior art method used to provide a graphics capability inside the package involves the use of a paper insert dropped with the product into the package during filling. When the consumer opens the package, the paper insert can be removed for viewing and use. This method has several drawbacks, however. The reliability of placing a single paper insert in each bag (by dropping the paper with a weighed amount of product) is a major consideration, particularly in small packages. A capacity issue is raised by the need to rent inserters to be used during the filling process. Foreign matter detectors are also frequently set off by the detection of the paper insert within the bag. The insertion of a piece of paper can raise the solvent level in the package beyond acceptable levels. All of the above greatly adds to the expense of each single package.
Another approach to this issue is illustrated in FIG. 1b, which is again a schematic cross-section of a packaging film. As with the embodiment shown in FIG. 1a, the embodiment shown in FIG. 1b comprises an outside OPP layer 10 followed by an ink layer 12, a laminate layer 14, and a metalized OPP or PET layer 16. However, an additional laminate layer 14′ is applied to the metalized layer 16 so that an additional ink layer 12′ and OPP or PET layer 10′ can be used as the new inside layer 10′. The use of the ink layers 12, 12′ as the second to last layer on both the outside and inside of the package allows for a full graphics capability on both the outside and the inside of the film. The additional film, however, adds approximately sixty percent (60%) to the cost of the material when compared with the embodiment shown in FIG. 1a. Overall capacity is also cut in half, since the film must be run through a typical converter twice. Further, since the material is 60% thicker, it cannot be run on a vertical form and fill machine at speeds as high as that used to make packages out of the embodiment shown in FIG. 1a. This is because longer dwell times must be used to form all the seals involved.
Another prior art approach to providing graphics within the bag would involve the application of the graphics directly to the inside metalized layer 16 shown in FIG. 1a. The application of such graphics can be accomplished using an inkjet printer. Food grade inks, however, do not adhere well to the inside metalized layer 16 because it is a low surface energy film. A low surface energy film is a film with a surface of less than 35 dynes/cm. Ink adhesion is poor on low surface energy films because the cohesive forces of the ink molecules have greater attraction to one another than to the inside metalized layer 16, causing the ink 47 to bead up as illustrated in FIG. 4a. The surface energy of the metalized inside layer 16 of FIG. 1a is approximately 30 dynes/cm whereas the wetting tension of the food grade inks is approximately 36 dynes/cm. Increasing the surface energy of the metalized inside layer 16 above the wetting tension of the food grade inks prevents the ink 47 from beading up (FIG. 4a). This increase in surface energy can be accomplished by treating the surface 46 with a flame or corona discharge. In FIG. 3, for example, a corona discharge is created by applying a high voltage from an electrode 32 to a dielectric 34. This generates ozone and when applied to the surface of the OPP layer 36 the surface energy of the OPP layer is increased which increases the adhesion force between the ink and the OPP layer allowing the ink to wet the layer, as shown in FIG. 4b, resulting in more permanent ink 48 contact. The treating of the inside layer 40, however, increases the melting point from a 180° F.-320° F. range for the untreated layer 46 to a 280° F.-320° F. range for the treated layer 40, which can result in longer dwell times which translates into slower production at the bagmaker, and the inability to produce an acceptable seal. Thus, sealing efficiency is greatly reduced when the treated layer 40 is used as a sealing surface. An additional risk occurs when sealing apparatus temperatures surpass 270° F. because of the risk that the outside OPP layer 10 in FIG. 1a may melt.
Another approach to solving this problem is to use a metalized inside layer 16 with a material that has a higher surface energy. For example, polyester or PET, has a surface energy of 43 dynes/cm. However, metalized OPP and PE films are less expensive than higher surface energy films such as polyester.
Consequently, a need exists for a package construction method and resultant package that allows for graphics that are available on the inside of a package upon opening of the package by the consumer that can be adapted to existing converter and form and fill packaging machines without reducing the capacity of either and that allows use of the lesser expensive metalized OPP film without compromising the sealing efficiency.